Spotlight Through Emperor Rudolf’s water tunnel under Letná
The Habsburg Emperor Rudolf II left a deep mark in Czech history. Various legends and myths surround the 16th century ruler who made Prague his imperial seat and whose diverse interests made the city a centre of Renaissance arts and sciences. One monument from his time is hidden beneath the surface of the earth – a water tunnel carved deep into the rock of one of Prague’s hills.
A small archway beneath the Vltava’s busy left embankment is closed with an iron bar. This is the southern entrance to a kilometre-long underground tunnel constructed more than 400 years ago during the reign of the legendary Emperor Rudolf II.
The tunnel runs under Letná hill, just across the river from Prague’s Old Town, and serves the function it was originally built for, supplying water from the Vltava to the ponds on the other side of the hill.
As we pass through the narrow entrance into the tunnel, wearing waders and helmets, my guide Jiří Pavlata from Prague’s water maintenance services instructs me how to walk properly on the tunnel’s uneven floor.
With the dark, muddy water of the Vltava up to our knees, we can see that the start of the tunnel is rather straight, and only begins to bend after several dozen metres. This, says my guide, is most likely due to fact that the composition of the rock which 16th century miners carved through is different at every stretch.
“I think they knew what they were doing and knew how to measure the route of the tunnel. But I think the rock just crumbled and they had to pass around it. I really don’t believe that they would make these turns for no reason.”
Says Jiří Pavlata, as we advance further into the dark. Some 40 metres above us, sitting literally on top of the tunnel, is the National Technical Museum. There, archivist Jan Hozák tells me about one of the most treasured items in the museum’s collection – the original plan of the tunnel, drawn on parchment in colours. It’s over two and a half metres long, and was made by the leading mining engineer of the time, Lazarus Ercker von Schreckenfels.
“This is a plan of a significant monument from the late Middle Ages which was built between 1583 and 1593. It is known as Rudolf’s water tunnel which connects the Vltava River with Stromovka Park which was then known as the royal game reserve. Rudolf II wanted the tunnel to supply water to fish ponds that were going to be established in the park, along with fountains and things like that.”
The tunnel took ten years to complete. Whenever the imperial coffers ran dry, construction was halted, and resumed when the Emperor again had money to spend. But the unstable and varied rock material presented a serious challenge for the miners brought in from the famous silver mines of Kutná Hora. Jan Hozák describes how the tunnel was excavated.
“They started by digging five vertical shafts along the route of the tunnel; the last of them was completed in 1588. They were around 190 metres apart but one of the shafts had to be backfilled because they struck a strong water spring. This was a big complication and delayed the whole project.”
Inside the tunnel, we pass several turns, and suddenly spot a beam of daylight coming from above. We are now under one of the shafts. I can see irons bars covering the shaft on the surface.
“This is one of the shafts which the miners used to start excavating the tunnel horizontally. People often think it’s just a sewage cover and throw garbage in but it stays on top of the vault and does not fall through into the tunnel. But every now and then, we have to get up there and clean it.”
Once a year, Jiří Pavlata and his men from the municipal water maintenance services clean the entire tunnel. They take out buckets full of river mud brought in with the water. The exhausting work takes about two weeks, and it’s not very pleasant because of the confined space and the dampness but also because of the rather strong smell of the mud. However, Jan Hozák says water in the Vltava used to be much dirtier in the past.
“The river was very dirty because all the workshops and factories that had been established in Smíchov and further up the stream released their waste into it. In the 19th century, the tunnel was part of a water supply system for the households on the other side of the hill but I’m sure people didn’t drink it.”
At one point, we come into a wider part of the tunnel where two mining crews digging from opposite directions met. However, they missed each other by a few metres and had to connect the two passages, creating a larger opening. It’s difficult to say whether this was caused by an error in calculation or by the poor quality of the rock. The workers were under close supervision and their progress was meticulously marked in the plan.
“When you look at the plan sideways, you see how far the miners advanced by a certain date. They are usually marked by six months periods; here you can see the date 31st of December, 1589, here is 1st July, 1590, and so on. The plan also provides an overview of the costs.”
The construction cost over 66,000 white Groschen, which was the local currency at the time. The costs were astronomical: the daily wages of a manual labourer at the time was around three or four Groschen while a glass of wine cost one Grosch, and a three-room house in Prague cost 420 Groschen. The plan of the tunnel also shows what that part of Prague looked like on the surface.
“What we know today as Letná plain had a different name at that time. It was called the Belvedere plain after a Renaissance palace near Prague Castle. When you look at this part which shows the end of the tunnel in Stromovka, you can see what the park looked like and you could even identify the individual trees. But the plain at the time was barren.”
The plan itself has an interesting history. Most of Emperor Rudolf’s Prague collections were looted during the Thirty Years’ War, including the large parchment with the plan of the tunnel. It appeared again in the late 19th century at an auction in Paris; Jan Hozák explains how it became part of the museum’s archive.
“We received the plan in 1908 from Prague’s Museum of Decorative Arts. The head of the museum bought it at an auction in Paris. We don’t know where the plan was for those three centuries. But when the Technical Museum was established, they gave it to us and now it’s the oldest and most precious items we have in our collections.”
After a good half-hour of wading through the tunnel, we slowly approach its other end at Stromovka park. The temperature noticeably drops and my guide Jiří Pavlata explains that as the cold air gets in here, the water in the tunnel sometimes freezes as far as some 50 metres from the entrance This part of the tunnel was in the past open to the public; however, it was damaged in the 2002 floods that hit the capital and for the time being, it will remain closed. But Jan Hozák from the National Technical Museum believes that perhaps in the future, the tunnel should be open again.
“I think people would be quite interested in visiting the tunnel, not just visitors but also local people. It’s quite an adventure to walk through the tunnel; it’s over a kilometre long, and it feels like you are in a mediaeval mine. So I think this would definitely be interesting but it would take a lot of money to make it safe.”
Although the tunnel is not likely to open for the public any soon, those interested in this fascinating monument now have a unique chance to see the original plan. The National Technical Museum is planning to exhibit the artefact to commemorate the 400th anniversary of Rudolf II’s death.
The episode featured today was first broadcast on January 18, 2012.